Sexual size dimorphism in anurans.

Area of Science:

• Zoology
• Evolutionary Biology
• Herpetology

Background:

• Sexual size dimorphism (SSD) is common in anurans, with females typically larger than males.
• Hypotheses often attribute this dimorphism to sexual selection, but life-history strategies remain under-explored.
• Understanding SSD drivers is crucial for anuran evolutionary and ecological studies.

Purpose of the Study:

• To test the hypothesis that anuran sexual size dimorphism is a function of sex-specific life-history strategies.
• To investigate the relationship between size dimorphism and age differences between sexes in anuran populations.
• To determine the relative importance of life-history differences versus sexual selection in shaping anuran SSD.

Main Methods:

• Compiled morphological and demographic data for anurans from existing literature.
• Calculated mean size and age for males and females across 51 populations (30 species, 8 genera).
• Employed statistical comparisons across species and genera, including phylogenetic independent contrasts for a subset of species.

Main Results:

• A significant positive relationship was found between the degree of size dimorphism (female-male size ratio) and the mean age difference between sexes.
• This relationship held true across different taxonomic levels (species, genera) and was supported by phylogenetic analyses.
• Differences in age structure between male and female anurans in breeding populations strongly correlate with size dimorphism.

Conclusions:

• Anuran sexual size dimorphism is largely explained by differences in the age structure of breeding populations, reflecting divergent life-history strategies.
• Life-history differences between sexes appear to be the primary driver of SSD in anurans.
• The role of sexual selection in anuran size dimorphism is likely secondary to life-history and age-related factors.